1. Field of the Invention
The invention concerns the field of high density reinforced reaction injection molded polyurethanes (RRIM), specifically microcellular or solid elastomers.
2. Description of the Prior Art
Reaction Injection Molding (RIM) is a technique for the rapid mixing and molding of large, fast curing urethane parts. High density RIM polyurethane parts are used in a variety of exterior body applications on automobiles where their light weight contributes to energy conservation. High density RIM parts are generally made by rapidly mixing active hydrogen containing materials with polyisocyanate and placing the mixture into a mold where reaction proceeds. These active hydrogen containing materials comprise a high molecular weight polyhydric polyether and a low molecular weight active hydrogen containing compound. The low molecular weight active hydrogen containing compounds are ethylene glycol, 1,4-butane diol or similar materials known to those skilled in the art.
Generally, the active hydrogen containing materials, both high and low molecular weight, are mixed together with catalyst and other optional materials in one tank and the polyisocyanate is contained in another tank. When these two streams are brought together in a mold, reaction is effected, and the RIM part is made. In many cases, in order to improve the strength properties of the RIM product, a reinforcing material such as chopped or milled glass or other mineral fibers is incorporated into the RIM formulation by placing the inert filler material in the unreacted components. Prior to our invention, the filler material for high density microcellular or solid RRIM urethanes has been placed in the active hydrogen containing material side, that is, the polyol side or split between the polyol side and the polyisocyanate side before the polyol and the isocyanate streams are mixed together.
Saidla's U.S. Pat. No. 4,073,840 discloses the placing of fibrous materials in polyurethane compositions with the placement of the fibrous material being optional between the isocyanate component and the polyol component. An example is given wherein the fibrous material is placed in the isocyanate component but with the proviso that the fibers could be alternatively added totally or partially to the second (polyol) component of the resin. Saidla is a broad disclosure which allegedly applies the concept of fiber placement in foamable compositions to many types of foams, including polyurethanes, epoxies and others. At column 6 of Saidla, beginning at about line 35, the preferred type of fiber reinforced material appears to be "reinforced structural foams." These are described as thick structural foam boards with thicknesses up to 3 inches. These appear to be rigid type polyurethane foams. At column 7 of Saidla, Table 1 describes foam materials which are 3.times.4" panels one inch thick, ranging in density from 21 to 43 pounds per cubic foot. Although it is not stated as such, these materials also appear to be rigid polyurethane foams. Also, at column 7 of Saidla, beginning at about line 33, low density foams containing fiber loadings are described wherein the core ranges from about 1 to 3 pounds per cubic foot and the skin ranges from about 30 to 60 pounds per cubic foot. Also, Saidla describes his materials as having a low density core and a high density integral skin. Indeed, the description at column 7, beginning at line 33, describes a foam with a skin density of at least ten times the core density and as much as 60 times the core density.
U.K. patent application No. 2,035,111 discloses a reaction injection molding process wherein glass fibers are incorporated into the raw materials before forming the part. This publication acknowledges the Saidla patent referred to above and states at page 1, line 100, that Saidla teaches placing the glass fibers into one or more of the resin components. The U.K. patent application discloses its invention at page 3, beginning at about line 71. According to the disclosure, the normal components A and B are supplemented by a separate auxiliary component system which contains the glass fiber filler material. At page 4, beginning at line 13, the U.K. patent application states that it is preferred to slurry the fiber in a separate portion of the polyol component.
It has been surprisingly discovered that properties are considerably improved if all of the inert filler material is placed in the isocyanate side prior to reaction for a high density microcellular or solid RRIM urethane.